The selective functionalization of aliphatic C-H bonds in complex organic molecules remains a most challenging problem in organic chemistry. Development of efficient methods to afford this transformation, in particular in the context of biologically active natural products, is bound to disclose unprecedented opportunities in the transformation of these molecules, thereby accelerating drug discovery efforts. In this application, we propose research aimed at developing powerful new methodologies to exploit P450 C-H oxidation catalysis and P450-mediated synthesis for selective transformation of unreactive aliphatic C-H bonds in complex natural products. To this end, efficient and time-effective strategies will be implemented to enable tailoring of the substrate reactivity, regio- an stereoselectivity of P450 monooxygenases and rapid generation of selective P450 catalysts for mediating functionalization of distinct unactivated aliphatic sites within a complex organic scaffold. At the basis of the proposed strategies there is a new enabling methodology to map the active site configuration in P450 monooxygenases and rapidly acquire information-rich functional profiles of these enzymes ('P450 fingerprints'). Systematic methods will be implemented to predict the reactivity of P450 variants via analysis of their fingerprints and to identify optimal mutagenesis schemes for altering the active site configuration in P450 monooxygenases without disrupting catalytic function. These new tools will be applied to obtain P450 catalysts with tailor-made regio- and stereoselectivity for hydroxylation of multiple aliphati positions in terpenes with clinically relevant anticancer and antimalarial activity. These efforts will unlock new avenues for late-stage transformation of these molecules in order to improve their pharmacological properties. By coupling selective P450-catalyzed aliphatic hydroxylations to chemical synthesis, novel and currently inaccessible derivatives of these natural products will be made available for activity evaluation. Through these studies, comprehensive structure-activity insights will be gleaned on these natural products, providing a basis for development of more potent antileukemic and antimalarial agents. Completion of the primary objectives of this application will result in a set of powerful and general strategies for P450 C-H oxidation catalyst development which will be readily applicable to a variety of other natural products and high- value compounds.